Basket centrifuge with self-triggering sludge discharge

ABSTRACT

A stationary skimming tube has its inlet orifice located at substantially the maximum radius of the sludge-accumulating space in the centrifugal bowl of a basket centrifuge. A sludge discharge pipe leading from the skimming tube has a normally closed valve; and located upstream from this valve is a restricted passage for discharging skimmed material from the tube. Means are provided for opening said valve in response to a pressure increase in the skimming tube resulting from sludge entering the restricted passage from the inlet orifice of the tube.

United States Patent [191 Conklin 1 Feb. 27, 1973 1 1 BASKET CENTRIFUGE WITH SELF- TRIGGERING SLUDGE DISCHARGE FOREIGN PATENTS OR APPLICATIONS 1,024,021 2/1958 Germany ..233/l9 R 387,636 2/1933 Great Britain ..233/21 Primary Examiner.lordan Franklin Assistant ExaminerGeorge H. Krizmanich Attorney-Davis, I-Ioxie, Faithful & Hapgood [57] ABSTRACT A stationary skimming tube has its inlet orifice located at substantially the maximum radius of the sludge-accumulating space in the centrifugal bowl of a basket centrifuge. A sludge discharge pipe leading from the skimming tube has a normally closed valve; and located upstream from this valve is a restricted passage for discharging skimmed material from the tube. Means are provided for opening said valve in response to a pressure increase in the skimming tube resulting from sludge entering the restricted passage from the inlet orifice of the tube.

3 Claims, 2 Drawing Figures CZAR/F/ED PRODUCT BASKET CENTRIFUGE WITH SELF-TRIGGERING SLUDGE DISCHARGE This invention relates to basket centrifuges and more particularly to a novel arrangement for automatically discharging separated slimes (hereinafter referred to as sludge) accumulated in the peripheral portion of the centrifugal bowl or basket of the centrifuge.

In prior basket centrifuges which sense when the separated sludge has accumulated to a certain level in the rotating bowl, it has been necessary to perform certain operations following such sensing, namely, shutting off the feed to the bowl which may or may not be accompanied by a reduction of the bowls rotational speed, and then operating a device for plowing accumulated sludge from the bowl, or else completely stopping the bowl after the feed shut-off and then removing the sludge manually.

The principal object of the present invention is to provide a basket centrifuge of the solid wall type in which accumulated sludge in the form of a slime is discharged from the bowl without the aforementioned operations.

In a basket centrifuge according to the invention, a stationary skimming tube has an inlet orifice located in the sludge space of the rotary bowl or basket near the peripheral wall thereof, and a sludge discharge pipe leading from this tube has normally closed valve. Upstream from this valve is a restricted passage for bleeding skimmed material from the tube, so that sludge entering the restricted passage from the tubes inlet orifice acts to increase the pressure in the tube; and means are provided for opening the aforementioned valve in response to a certain pressure increase in the tube, whereby sludge is discharged through the valve and sludge discharge pipe.

Preferably, the restricted passage bleeds skimmed material into the stationary duct through which the mixture of sludge and liquid is fed into the rotary bowl.

For a better understanding of the invention, reference may be had to the following detailed description in conjunction with the accompanying drawing, in which: FIG. 1 is a schematic view, partly in vertical section, of a preferred form of the new centrifuge with parts broken away, and FIG. 2 is a schematic view of a modification of the means forming the restricted bleed passage from the skimming tube.

The basket centrifuge as shown in FIG. 1 comprises a centrifugal bowl of the solid wall type (i.e., its outer or peripheral wall is unperforated). A central nave 10a of the bowl bottom receives the tapered upper end of a shaft or spindle 11 which supports the bowl and which is driven by a suitable motor (not shown) so as to rotate the bowl on a central vertical axis. The shaft 11 is supported laterally by bearings 12 mounted in a stationary housing 13 containing the bowl, this housing being closed at the top by a cover piece 13a.

The mixture to be separated is delivered to a stationary feed tube 15 extending centrally through the cover piece 13a and through a central opening in the top of bowl 10. A cone l6 surrounds the bowl nave 10a and is held in spaced relation thereto by small radial Wings 17. The feed from pipe 15 flows downward through the annular passage 18 between cone l6 and the bowl nave 10a, the feed stream then entering the separating chamber of the bowl. In this chamber, the feed is brought up to the bowl speed by means of large radial wings extending inwardly from the peripheral wall of the bowl, one of these wings being shown at 19. The heavier portion of the feed builds up as a slime against the peripheral wall of the bowl under the action of centrifugal force, and the liquid constituting the lighter portion of the feed builds up radially inward of the slime until it reaches the edge of the top opening 20 which forms an over-flow outlet. The clarified liquid product discharges from the over-flow outlet 20 into the stationary housing or hopper l3 and discharges from the latter through a bottom outlet 1317.

A stationary skimming tube 22 extends downwardly through the stationary cover piece 13a and through the underlying top opening 20 of the bowl. The inlet end 22a of this tube is located near the peripheral wall of the bowl, that is, at substantially the maximum radius of the sludge space in which the slime accumulates during the centrifugal separation of the mixture in the separating chamber of the bowl. As shown in FIG. 1, the inlet opening or orifice 22a of the skimming tube faces in a direction opposite to the direction of rotation of the bowl so that the tube can perform its skimming function. Also, the horizontal portion of the skimming tube 22 within the bowl, as shown, is located somewhat above the upper ends of the radial wings 19. The upwardly extending portion of skimming tube 22 leads to a sludge discharge pipe 23 in which a normally closed valve 24 is inserted. Upstream from valve 24 is a branch pipe 25 leading from skimming tube 22, this pipe being provided with means 26 forming a restricted passage for bleeding skimmed material from tube 22 into the stationary feed pipe 15.

An upward extension 27 of skimming tube 22 is provided with a conventional device 28 for sensing pressure changes in the skimming tube. These pressure changes are transmitted from the sensing device 28 to an indicating controller 29 by way of an operative connection shown by a broken line at 30. The valve 24 is actuated by a conventional motorized or diaphragm unit 31, and the latter is operatively connected to the indicating controller 29 as shown at 32.

The new basket centrifuge is intended for separation of a mixture of a liquid and solids suspended therein and which, when separated from the liquid, constitute a slime which remains in a flowable state as a heavier component. For. example, during so-called electrochemical machining, the electrolyte becomes contaminated with small quantities of metal hydroxides which are not crystalline in structure but rather are slime; and since the electrolyte is a rather costly item, it is important that the electrolyte be recovered in as pure a state as possible. On the other hand, the slimes are in relatively short supply (and often of only slightly greater specific gravity than the electrolyte), so that provision must be made to hold them in the bowl for as long as possible in order to separate the maximum amount of electrolyte therefrom before discharging the slimes from the bowl.

Assuming by way of example that the above-mentioned mixture of electrolyte and slimes is to be separated, the mixture enters the separating chamber of bowl 10 as previously described, the liquid level eventually reaching the over-flow outlet 20 as the feed continues. Initially, the stationary tube 22 will pare liquid electrolyte from the rotating mass in the bowl,

the pared liquid flowing at a low rate through restricted orifice 26 in branch pipe 25. Since this pared liquid is bled back to feed pipe 15, no electrolyte is lost during this initial operation. When the separated slimes accumulate sufficiently in the outer peripheral portion of the separating chamber, they enter the inlet orifice 22a of the skimming tube and pass through the restricted orifice 26, with the result that the pressure in skimming tube 22 is substantially increased due to the fact that the slimes flow less readily than the liquid electrolyte through the restricted orifice 26. This increased pressure in tube 22 is transmitted from the sensing device 28 through connection 30 to the indicating controller 29, causing the latter to open the valve 24 through its motorized unit 31. The pared slimes are then discharged through pipe 23 to waste. Since the slimes constitute only a minor portion of the feed stream and are retained within the bowl for an extended period of time, they are discharged at a low flow rate in concentrated form (i. e., essentially free of electrolyte). On the other hand, the liquid electrolyte is discharged from the bowl at a relatively high flow rate by way of the overflow outlet 20.

Whenever the level of accumulated slimes recedes outwardly from the inlet orifice 22a of the skimming tube, the flow of slime through the restricted passage 26 will cease and will be replaced by a flow of liquid electrolyte through this passage. The resulting pressure decrease in skimming tube 22 is sensed by the device 28 and transmitted through connection 30 to the indicating controller 29, whereby the valve 24 is reclosed by its motorized unit 31. Thus, flow through the sludge discharge pipe 23 is now arrested until the separated slimes again build up to the level of the paring tube orifice 22a, thereby causing the valve 24 to reopen in the manner previously described. However, under normal operating conditions, once the valve 24 is opened in response to a sufficient accumulation of slimes in the peripheral sludge space of the bowl, this valve will remain open as the pared slimes are replaced by newly separated slimes from the continuous feed stream entering the separating chamber of the bowl, until the run is completed.

Due to the return of electrolyte from skimming tube 22 through the restricted passage 26 and feed tube to the separating chamber of the bowl, an extended period of time may be required before normal discharge of clarified electrolyte would start at the oven-flow outlet 20.

The invention also includes a means for periodic sludge removal without the use of an automatic controller. Should intermittent draw-off of the accumulated sludge be desirable, the valve 24 can be replaced by an adjustable relief-type valve 24' (see FIG. 2) suitable for intermittent operation, and a spring-loaded check valve 34 can be inserted in branch pipe 25 ahead of the orifice 26.

The relief valve 24' will be set to open at a pressure that will insure a concentrated sludge draw-off. The check valve 34 in series with the orifice 26 in branch pipe 25 will prevent a reverse flow of feed material from feed pipe 15 through branch pipe 25 to pipe 22 when valve 24' discharges. Such an arrangement does not require the use of a relatively expensive controller 29 and an air-o eratedmodulated valve 24.

In addition 0 clarifying electrolyte from electrochemical machining operations, the new basket centrifuge is suitable for clarifying other mixtures such as yeast suspensions, wine bottoms and activated waste sludge.

The previously mentioned components 28, 29 and 24, 31, are conventional instruments. For example, the device 28 may be a pneumatic pressure transmitter such as that known as Moore GC-17. The indicating controller 29 may be one known as Moore (EC-50, which responds to an air pressure signal of 3-l5 psi. The valve 24 and its motorized unit 31 may be 'a diaphragm valve known as Taylor 203 VA 321.

lclaim:

l. A basket centrifuge comprising a centrifugal bowl mounted for rotation about an axis, a feed tube for supplying a mixture of liquid and solids to the bowl, a stationary housing containing the rotor and adapted to receive liquid centrifugally separated as a light component from said mixture in the bowl, the bowl having an outer peripheral space for accumulating sludge separated as a heavy component from the mixture, a stationary skimming tube having an inlet orifice located in said sludge space at substantially the maximum radius thereof, a heavy component discharge pipe leading from the skimming tube, a normally closed valve in the heavy component discharge pipe, means forming a restricted passage for bleeding skimmed heavy component from said tube at a location upstream from said valve, whereby sludge entering said restricted passage from the inlet orifice acts to increase the pressure inthe skimming tube, and means responsive to increase of said pressure to a predetermined valve for opening said valve and thereby discharging heavy sludge component from said outer peripheral space by way of said tube and discharge pipe.

2. A centrifuge according to claim I, in which said restricted passage communicates with said feed tube and thereby returns the bled material to said feed tube.

3. A centrifuge according to claim 1, in which said passage-forming means include a check valve operable to open said passage in response to increase of the pressure in said tube to a pressure less than said predetermined value. 

1. A basket centrifuge comprising a centrifugal bowl mounted for rotation about an axis, a feed tube for supplying a mixture of liquid and solids to the bowl, a stationary housing containing the rotor and adapted to receive liquid centrifugally separated as a light component from said mixture in the bowl, the bowl having an outer peripheral space for accumulating sludge separated as a heavy component from the mixture, a stationary skimming tube having an inlet orifice located in said sludge space at substantially the maximum radius thereof, a heavy component discharge pipe leading from the skimming tube, a normally closed valve in the heavy component discharge pipe, means forming a restricted passage for bleeding skimmed heavy component from said tube at a location upstream from said valve, whereby sludge entering said restricted passage from the inlet orifice acts to increase the pressure in the skimming tube, and means responsive to increase of said pressure to a predetermined valve for opening said valve and thereby discharging heavy sludge component from said outer peripheral space by way of said tube and discharge pipe.
 2. A centrifuge according to claim 1, in which said restricted passage communicates with said feed tube and thereby returns the bled material to said feed tube.
 3. A centrifuge according to claim 1, in which said passage-forming means include a check valve operable to open said passage in response to increase of the pressure in said tube to a pressure less than said predetermined value. 